A pulse combustion apparatus comprises (i) a combustion section or sections each chiefly including a burner, a combustion chamber, a tail pipe and an exhaust muffler and (ii) an air supply section chiefly including an air blower and a supply muffler. In the apparatus combustion repeats itself many times. To be more exact, in the apparatus a series of air/fuel mixture supply, explosion, combustion, expansion and exhaust occurs in some 60 to 150 cycles per second. In use, the combustion chamber and the tail pipe are disposed within a tank (hot-water tank or oil tank) of a machine, such as a hot-water-storing type hot water supply machine, a fryer, or a noodle boiling machine. With a pulse combustion apparatus, it is almost impossible to control the combustion capacity of the burner of the combustion section, especially due to the construction and the combustion manner of the apparatus. Thus, with a pulse combustion apparatus having only one combustion section, it is almost impossible to control the quantity of the heat produced by the apparatus. Therefore, where there is the necessity for such a controllability, a pulse combustion apparatus with two or more combustion sections is produced. With such an apparatus, it is possible to control the quantity of the heat produced thereby by causing combustion to take place in all the combustion sections at one time and in only one or more of the combustion sections at another time.
One example of a prior art pulse combustion apparatus with such a construction is shown in FIG. 3. The apparatus of FIG. 3 includes a pair of combustion sections A each having a combustion chamber 2 and an air supply section B which supplies air into each combustion chamber. The air supply section B includes (i) an air blower F with a supply outlet 13, (ii) a supply muffler 10, (iii) a pair of air introducing channels 11 and (iv) a pair of air chambers 12. The construction from the supply outlet 13 to the air chambers 12 provides a single air admitting passage C for common use by the two combustion sections A. The rotating speed of the air blower F and, hence, the rate of supply of air of the supply section B into the combustion chambers 2 are set at a given value required for combustion in both the combustion chambers 2. Thus, initially, combustion certainly can be started, as desired, in one or both of the two combustion chambers 2. And once combustion starts in each chamber 2 in a steady state, each chamber 2 is "self-sustaining", or draws, by itself, the air within the section B into itself thanks to the negative pressure which is created, within the chamber 2, by the combustion products produced therein and flowing toward an exhaust pipe. In other words, once proper combustion takes place in each section A, each section A is automatically supplied with the air without operating the blower F. However, if and when the blower F is restarted to start or restart combustion in one of the combustion chambers 2 while combustion is taking place only in the other combustion chamber, the "inactive" combustion chamber is only supplied with an amount of air which is considerably smaller than that predetermined by the rotating speed of the blower F. The reason for this is that the bulk of the air from the blower F is drawn by the "active" combustion chamber because of the above-mentioned "self-sustaining" character of the "active" combustion chamber. Thus, in such a case, the ignition of the air/fuel mixture does not take place as expected, or is delayed, in the "inactive" chamber.
In order to obviate such a defect, the applicant has proposed, in Japanese Patent Application No. 62-86503, a pulse combustion apparatus whereby an air blower is rotated at a speed higher than the normal, or fundamental speed when combustion is to be started or restarted in an "inactive" combustion chamber while it is taking place only in another combustion chamber, thereby supplying the "inactive" combustion chamber with the amount of air which enables proper combustion to take place in it even in such a state. However, such a proposal calls for the provision of a means for determining when combustion is to be started or restarted in the "inactive" combustion chamber, as well as the provision of a means for increasing the rotating speed of the blower.